Terminal branching of the cochlear nerve fibers: The cochleas of newborn guinea pigs are stained by the Golgi method. Pieces of the cochlear duct containing single well-stained nerve fibers are embedded in araldite and serial thin sections analyzed by electron microscopy. At present this seems to be the most reliable method for characterizing the branching of single cochlear nerve fibers. Effects of ethacrynic acid on the memebranous labyrinth: Guinea pigs will be given 40 mg/Kg of the drug I.V. and sacrificed at 5 hours, 3, 5 and 10 days post-drug to fill out our present experimental series. Cochlear potentials (C.M. or E.P.) will be monitored before fixation. Other animals will be given a smaller dose daily for 5-7 days and sacrificed at 1 and 2 weeks after the last dose. Both cochlear and vestibular memebranous labyrinth will be studied by ordinary light and electron microscopy for pathology.